This thesis explores the meaning and significance of sibling and peer relationships for young people looked after by local authorities, from their own perspectives. A sociological approach to research with young people is employed, drawing on additional post structural and feminist insights. It is argued that hegemonic ideas concerning the nature of development have resulted in a concentration on adult and adult-child relationships, from adult perspectives. Accordingly, children‟s perspectives on the contribution of their interrelationships to their well-being, support networks, and sense of social inclusion have not been adequately theorised. It is concluded that this has had particular implications for looked after children, as the process of becoming and remaining looked after can result in considerable losses within their sibling and peer relationships.\ud A participatory methodology was developed in order to address issues of power, agency and choice within the research process. Qualitative interviews were undertaken with eighteen young people, aged between twelve and nineteen, who were, or had previously been, looked after. Sibling and peer relationships were found to make significant contributions to the young people‟s emotional and physical well-being, and sense of individual and familial identity, as well as providing emotional and practical support into adulthood. Accordingly, the loss of significant relationships, particularly those with siblings, could affect them deeply.\ud While living in care, the young people were often optimistic about the ease of negotiating relationships with siblings and friends after leaving care. However, in reality, living independently could amplify problems within sibling and peer relationships, placing young people at risk of homelessness, violence, and social isolation.\ud This thesis contributes greater understanding of the importance of a wide variety of sibling and peer relationships to the lives of looked after children, from their own perspectives. It also informs as to the complex challenges they face both during and after leaving care in negotiating their sibling and peer relationships in the interests of their emotional and physical well-being.